The present invention is a device for unloading silage from a tower silo. More specifically, the present invention relates to a silo unloader used to remove silage from a tower silo and transfer it to a chute extending to the base of the silo.
Top unloading silo unloaders are well known in the art as a method for removing silage from a tower silo (more specifically, a cylindrical tower silo). Generally speaking, the silage is loaded into the silo by simply piling it from the bottom up. When it becomes time to remove silage from the silo (so as to feed livestock etc.), a top unloading silo unloader is lowered onto the silage. The unloader then transfers silage from the interior of the silo to a chute which extends from the top to the bottom of the silo, along an exterior side thereof. The unloader utilizes an auger mechanism which is placed directly upon the silage. The auger operates to pull silage in a uniform manner toward the center of the silo. At the center of the silo unloader is a blower mechanism which receives the silage and propels it through a spout to the aforementioned exterior chute.
There are many commonly known "styles" of top unloading silo unloaders. A single auger device incorporates one auger which is placed on the silage and pulls silage into the center of the silo. A blower is then used to propel silage up and out of the silo.
Several problems exist with single auger silo unloaders. First, when silage is extremely hard (either compacted or frozen), a single auger is not always effective at breaking up the silage and drawing it toward the center of the silo. In extremely frozen conditions, the single auger unloader has a tendency to become ineffective at cutting loose frozen silage and start jumping and bouncing and can actually break components on the unloader.
Top loading silo unloaders generally have mechanisms which allow them to be placed within the round silo tower and then rotate or pivot about the center of the tower. Ideally, the auger arm will evenly cut through all of the silage and uniformly remove it from the silo. More specifically, the silo unloader will not remove silage from one side of the silo at a greater rate than the other side, thus creating an uneven or substantially unlevel upper surface of the silage. A number of things must happen as this auger arm rotates around the silo in order to effectively unload the tower silo. First, as previously mentioned, the auger arm must evenly remove and cut through the silage as it is removed. This becomes extremely difficult, however, when the silage becomes very hard due to either compaction or freezing. Secondly, silage must be evenly removed from the center point so as to avoid the creation of a mound or "plug" at the center or pivot point within the silo below the single auger blower. Also, silage must be removed right up to the walls, thus not leaving additional amounts of silage frozen to or attached to the walls.
Also important in the operation of a silo unloader are all the usual concerns regarding efficient operation (both from a power or energy consumption perspective and a silage transfer rate perspective). A typical farmer would like to move silage at a very high rate and use small amounts of power to do so. Also, as farms continue to get larger, it is very important for the farmer to remove silage at a higher rate (typically the farms of today have more livestock than in previous years).
Another common problem with the aforementioned single auger silo unloaders comes from their use of a closed cavity blower. The blowers generally used in silo unloaders are similar to any other fan or blower mechanism used in numerous material transfer situations. Generally, the blower has a rotating shaft with a number of blades attached thereto. The shaft and blades are configured within an enclosed cavity with an inlet port and outlet port. Silage is then fed into the inlet by some mechanism (usually augers or flipping blades), is engaged by one of the blower blades, and is propelled out the blower outlet port. Attached to the outlet is generally a silage directing spout which will then direct the silage out of the silo. In most single auger silo unloaders, the blower inlet is located on one side of the blower and the outlet is located on a top portion (the side and top defined such that the side is a surface or plane which is perpendicular to the axis of rotation whereas the top is a portion which is parallel to the axis of rotation).
In operation, the single auger silo unloader has its aforementioned auger rotating to draw material toward the center of the tower silo while advancing in the direction opposite the auger rotation. Situated at the center is the blower mechanism which is positioned such that silage is propelled into its inlet. The auger arm or auger assembly then rotates around the tower silo to evenly and uniformly unload material. As this entire mechanism rotates around, the enclosed bottom portion of the blower assembly tends to contact and compact the silage at the center of the silo. Furthermore, due to the alignment of the auger and transfer blades within the silo, this compacted material is not usually engaged by the auger. Therefore, a compacted mound is created which cannot be easily removed by the silo unloader.
In summary, the single auger silo unloader is not desirable because it lacks aggressiveness to break up compacted or frozen silage, and it also tends to create a compacted mound or hill at the center point of the silo under the blower.
A second type of top unloading silo unloader utilizes two augers to draw material toward the center of silo (otherwise known as a double auger silo unloader). This type of design is very desirable in removing compacted or frozen silage as the two augers can work in conjunction with one another to very aggressively break up the silage. Generally, the two augers will be placed parallel one another and will be configured to rotate in opposite directions. This has numerous advantages in removing the silage. By rotating in opposite directions, the rotation of the augers will not tend to pull the auger arm in any specific direction. Stated alternatively, the pulling forces created by the rotation of each auger will tend to cancel out one another. Further, the two augers can be sized differently so as to cut at different depths. This creates more efficiency because each auger is attempting to shave off only a limited amount of material thus allowing the second auger to cut a little bit deeper. As would be expected in the use of two augers, this auger arm is capable of moving much more material or silage at any given time during frozen or hard packed conditions. Conversely, in long cut summer conditions the front auger can be too aggressive and have a tendency to pull the unloader off center.
Usually, as stated above, the augers are placed parallel one another and rotate to pull material toward the center of the silo. Located at the center is a blower assembly for picking up and propelling the silage out of the silo. This blower is configured differently from that of the aforementioned single auger blower however. Due to the configuration of the two augers, it has been found advantageous to put the blower between the two augers. Also, the blowers generally used in this application have an open bottom configuration. In this open bottom configuration, the blower blades are allowed to extend out of the blower housing and directly contact the silage (as opposed to the configuration used in a single auger where the silage material is propelled into a blower inlet). In this configuration the dual augers simply pull silage toward the center of the tower by moving material between the two augers. By placing the open bottom blower between the two augers, these augers naturally propel material to a position where the blower can then interact with the silage and propel it out of the silo.
The open bottom configuration has a second advantage of avoiding the aforementioned compaction created by closed bottom blowers. By having an open bottom, the blower is actually allowed to contact the silage and break it up. This action avoids any compaction or mounding in the center of the silo itself. But one major drawback of this type is that it requires a log more horsepower to run than the enclosed bottom blower.
The use of a double auger silo unloader does not come without its price, however. As mentioned, the open bottom blower is positioned between the two augers. As would be expected, this requires the augers to be spaced a sufficient distance apart from one another so as to allow the positioning of the blower therebetween. This separation requirement increases the width of the auger arm that is used. Remembering that this auger arm rotates around the silo by pivoting at a center point. It is desirable to keep this auger arm as narrow as possible thus allowing efficient rotation and removal of silage from the silo. By utilizing a wider auger arm, misalignments are more easily encountered, resulting in jamming or undesirable forces to be placed on the auger especially in a smaller diameter silo. The width will not allow a single point to extend out to the wall of the silo and remove material therefrom. While each side of the unloader will reach the wall, there will then be a portion or extension between the two augers where a gap exists between the auger arm and the silo wall. This is undesirable as compaction and inefficient removal of silage can occur. Under winter conditions a frozen ridge may form that can make the unloader hang up.
Secondly, the use of an open bottomed blower mechanism, while achieving some advantages, is not very efficient. Energy is lost each time the blower contacts the silage itself and slaps or bangs into any compacted silage. Also, by having an open bottom, the handling of silage by the blower is also not very efficient. As is known by those who deal with fans or material transfer mechanisms, tighter tolerances between the fan or blower blades and the walls of the blower, results in more material being efficiently moved. By utilizing an open bottom blower, material is allowed to fall off either side of the blade and also off the bottom of the blade. Both of these characteristics of an open bottom blower rob both power and efficiency from this type of blower mechanism. Therefore, when the farmer compares the amount of material transferred with the amount of energy used, they may find that they are paying a lot of money in energy costs to transfer silage using this mechanism.